Abstract
The crystal structures and microstructures of parent and martensite phases of Au7Cu5Al4 alloy were investigated using X-ray diffraction and transmission electron microscopy. Premartensitic tweed striations with 6 M modulated structures were observed in the austenitic phase. Non-modulated martensite variants and partially modulated (8 M) martensite variants were found in the alloy that was slowly cooled (10 K/min) to –10 ℃. By contrast, in addition to non-modulated martensite plates, perfect periodic modulated (8 M) martensites were observed when the alloy was quenched into liquid nitrogen. The crystal structures of martensites with or without modulation can be basically indexed with a body-centered tetragonal (bct) structure. Whereas the tetragonality ratio (c/a) for the martensite was found to be affected by the modulation structure. These results resolve the controversy regarding the structure of martensite.
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